1. Field of the Invention
The invention relates to a vibration damper with variable damping force including a cylinder filled with damping medium and a piston fastened to a piston rod arranged in an axially movable manner and dividing the working cylinder into two working spaces, the damping force for the directions of rebound and compression being influenced by nonreturn valves acting in the respective direction and a damping valve of variable damping action.
2. Description of the Related Art
A prior art hydraulic adjustable vibration dampers in which the cylinder filled with a damping medium is divided by a damping piston into two working spaces are known, for example, from German reference DE 35 18 327 C2. The damping piston includes damping valves for the directions of rebound and compression which provide a basic damping of the vibration damper. In addition, a bypass connection is arranged between the lower and upper working spaces in which a pressure-dependent valve and an adjustable valve, actuated by an electromagnet, are provided in series. The adjustable valve provides for the opening and closing of the bypass, while the spring-loaded valve allows the damping medium to pass when the bypass is open and when a specific basic pressure is reached. These two series-arranged valves are respectively active in the rebound and compression stages and operate parallel to the damping valves in the actual damping piston.
A further prior art vibration damper is known from German reference DE 196 24 895 C1 which comprises a cylinder filled with damping medium and in which a piston rod with a piston is configured in an axially movable manner, the piston dividing the cylinder into two working spaces and having appropriate valves for the basic damping. Additionally provided in a bypass at the outer circumference of the cylinder is a pressure-dependently active damping valve, the damping force of which acts on a shut-off valve body against a spring force, by means of an actuator. This damping valve is arranged hydraulically in series with an inlet valve with its own damping action, so that the action of the variable damping valve is superposed with the inlet valve.